Atherosclerosis is a complex, progressive and degenerative condition resulting in the build-up of cholesterol and other obstructive materials, known as plaque, on the walls of the arteries. The accumulation of plaque narrows the interior or lumen of arteries, thereby reducing blood flow. Plaque occurs in the arteries in several different forms and may be located in many different anatomies throughout the arterial system. Plaque varies in composition, with portions that are hard and brittle, referred to as calcified. plaque, and other portions that are fatty or fibrous. Over time atheromatous deposits can become large enough to reduce or totally occlude blood flow through the vessels, leading to symptoms of low blood flow, such as pain in the legs (during walking or at rest), skin ulcer, angina, and other symptoms.
Chronic Total Occlusions (CTOs), are usually hard calcified plaque blocking all blood paths through the vessel, and are found in a large percentage of the patients. To treat this disease and improve or resolve these symptoms it is desirable to restore or improve blood flow through the vessel.
Various means are used to restore or improve blood flow through atheromatous vessels. The atheroma deposits can be displaced by diametrically expanding the vessel by inflating balloons, expanding stents, and other methods.
The plaque can be pulverized using lasers and other methods however pulverization alone of atheromatous material may allow micro-emboli to flow downstream and lodge in distal vascular beds, further compromising blood flow to the tissue affected by the disease.
Many types of atherectomy catheter devices have been proposed, including catheters with rotating burrs, lasers to photo-dissolve tissue, catheters with ultrasonic vibration mechanisms, and catheters which use balloons or other positioning features to position the cutter adjacent material to be removed.
Most of current CTO crossing devices or atherectomy devices are led over standard guidewires, preventing them from exit the vessel walls while moving forward removing the plaque. This means that a thin guidewire, usually between 0.014″ to 0.035″ in diameter, must first cross the total occlusion. Special crossing guidewires are available today, so-called CTO wires, designed especially to cross plaque material, including calcified and hard plaque material.
Few crossing or atherectomy devices do not ride over a guidewire, but then they must have some sort of imaging system and/or controlled maneuverability and bending capabilities, to keep inside the blood vessel lumen, preventing vessel perforation. Such mechanism or imaging systems significantly increase their cost.
The CTO proximal cap is usually the harder part of the occlusion, and if the guidewire or crossing device can penetrate the CTO proximal cap, they usually can cross the whole length of the CTO.
Still in about 20% of the peripheral CTO patients, the CTO proximal cap is too hard and impossible to penetrate for any guidewire and/or crossing device. The only options for the physician in such cases is to cross the CTO sub-intimally, probably using expensive lumen reentry devices, or use the relative complex retrograde technique and cross the occlusion from the distal cap, which is usually softer then the proximal cap.